The invention relates to a coupling device for a low-rate carrier current transmission system, comprising a control circuit, means for supplying power to the control circuit via an AC electrical power distribution system and means for coupling the control circuit to the electrical power system for transmission and receipt of modulated information transmitted by carrier current over the power distribution system, the power supply means comprising a transformer having a primary winding connected to the power distribution system and a secondary winding connected to the control device.
Low-rate carrier currents, i.e. for a transmission rate lower than 100 kbits/s, for example at 2,400 bits/s, are used in particular in home automation systems for control and/or monitoring of electrical equipment by means of an AC electrical power distribution system (for example 230V and 50 Hz).
Conventional coupling devices generally comprise an isolated power supply designed to supply the electrical power necessary for the coupling device components from the electrical power distribution system. Moreover, an isolated magnetic coupler enables transmission and receipt of modulated information from the electrical equipment to the electrical power system and vice-versa. For safety of persons, both the transformer and the magnetic coupler have to provide a good electrical isolation between the electrical equipment and the electrical power system.
The object of the invention is to provide a reduced cost coupling device, while achieving a good electrical isolation between the electrical equipment and the electrical power system.
According to the invention, this object is achieved by the fact that the power supply means comprise a two-way switch connected in series with the primary winding, the control circuit comprising means for detecting the presence of a carrier connected to the terminals of the secondary winding, the device comprising an optocoupler controlling the two-way switch and a three-position selector switch controlled by the control circuit, the selector switch having an output connected to a control input of the optocoupler, a first input connected to an output of an oscillator, a second input connected to a transmission output of the control circuit, and a third input connected to an output of preset DC voltage of the power supply means, the output of the selector switch being connected to the first input in standby mode so as to define a preset switching frequency of the power supply means, to the second input in transmission mode so as to modulate the information to be transmitted, and to the third input in receipt mode when the control circuit has detected the presence of a carrier in standby mode.